Synoptic reconstruction of a major ancient lake system: Eocene Green River Formation, western United States

Abstract

Numerous 40 Ar/ 39 Ar experiments on sanidine and biotite from 22 ash beds and 3 volcaniclastic sand beds from the Greater Green River, Piceance Creek, and UintaBasins of Wyoming, Colorado, and Utah constrain ~8 m.y. of the Eocene Epoch. Multiple analyses were conducted per sample using laser fusion and incremental heating techniques to differentiate inheritance, 40 Ar loss, and 39 Ar recoil. When considered in conjunction with existing radioisotopic ages and lithostratigraphy, biostratigraphy, and magnetostratigraphy, these new age determinations facilitate temporal correlation of linked Eocene lake basins in the Laramide Rocky Mountain region at a signifi cantly increased level of precision. To compare our results to the geomagnetic polarity time scale and the regional volcanic record, the ages of Eocene magnetic anomalies C24 through C20 were recalibrated using seven 40 Ar/ 39 Ar ages. Overall, the ages obtained for this study are consistent with the isochroneity of North American land-mammal ages throughout the study area, and provide precise radioisotopic constraints on several important biostratigraphic boundaries.Applying these new ages, average sediment accumulation rates in the Greater Green River Basin, Wyoming, were approximately three times faster at the center of the basin versus its ramp-like northern margin during deposition of the underfi lled Wilkins Peak Member. In contrast, sediment accumulation occurred faster at the edge of the basin during deposition of the balanced fi lled to overfi lled Tipton and Laney Members. Sediment accumulation patterns thus refl ect basin-center-focused accumulation rates when the basin was underfi lled, and supply-limited accumulation when the basin was balanced fi lled to overfi lled. Sediment accumulation in the Uinta Basin, at Indian Canyon, Utah, was relatively constant at ~150 mm/k.y. during deposition of over 5 m.y. of both evaporative and fl uctuating profundal facies, which likely refl ects the basin-margin position of the measured section. The most rapid sediment accumulation for the entire system (>1 m/k.y.) occurred between 49.0 and 47.5 Ma, when volcaniclastic materials from the Absaroka and/or Challis volcanic fi elds entered the Green River Formation lakes from the north.Our new ages combined with existing paleomagnetic and biostratigraphic control permit the fi rst detailed synoptic comparison of lacustrine depositional environments in all the Green River Formation basins. Coupled with previously published paleocurrent observations, our detailed correlations show that relatively freshwater lakes commonly drained into more saline downstream lakes. The overall character of Eocene lake deposits was therefore governed in part by the geomorphic evolution of drainage patterns in the surrounding Laramide landscape. Freshwater (overfi lled) lakes were initially dominant (53.5-52.0 Ma), possibly related to high erosion rates of remnant Cretaceous strata on adjacent uplifts. Expansion of balanced-fi ll lakes fi rst occurred in all Green River Formation basins ...

Mammals from the earliest Uintan (middle Eocene) Turtle Bluff Member, Bridger Formation, southwestern Wyoming, USA, Part 3: Marsupialia and a reevaluation of the Bridgerian-Uintan North American Land Mammal Age transition

“…Of the two dated samples in this study, the date of sample PCM3Aug14-04 from the tuffaceous white sandstone bed is in close agreement with the U-Pb date of the Sage Creek Mountain tuff by Tsukui (2016), and the two ages overlap within analytical error. These two U-Pb dates are also in agreement with the 40 Ar/ 39 Ar date of Smith et al (2008Smith et al ( , 2010 for the Sage Creek Mountain tuff when the astronomically calibrated age of the Fish Canyon sanidine is used, although the 40 Ar/ 39 Ar date is comparatively older. Based on the age as well as the description of the bed from which the sample was collected, it is likely that the Sage Creek Mountain tuff of Smith et al (2008Smith et al ( , 2010 and Tsukui (2016) is the same bed as the bed from which PCM3Aug14-04 was collected.…”

“…These two U-Pb dates are also in agreement with the 40 Ar/ 39 Ar date of Smith et al (2008Smith et al ( , 2010 for the Sage Creek Mountain tuff when the astronomically calibrated age of the Fish Canyon sanidine is used, although the 40 Ar/ 39 Ar date is comparatively older. Based on the age as well as the description of the bed from which the sample was collected, it is likely that the Sage Creek Mountain tuff of Smith et al (2008Smith et al ( , 2010 and Tsukui (2016) is the same bed as the bed from which PCM3Aug14-04 was collected. The best age estimate for the Ui1a fauna in the TBM is thus provided by the radioisotopic (U-Pb and 40 Ar/ 39 Ar) dates from the level of Locality SDSNH 5844 (Roll the Bones) as well as the stratigraphically lower tuffaceous white sandstone bed and the apparently laterally equivalent Sage Creek Mountain tuff.…”

“…The new radioisotopic data provide important constraints for the age of the TBM as well as its Ui1a fauna. The new U-Pb dates are generally consistent with the U-Pb and 40 Ar/ 39 Ar ages of ash beds from the Bridger Formation in Smith et al (2008Smith et al ( , 2010 and Tsukui (2016). Of the two dated samples in this study, the date of sample PCM3Aug14-04 from the tuffaceous white sandstone bed is in close agreement with the U-Pb date of the Sage Creek Mountain tuff by Tsukui (2016), and the two ages overlap within analytical error.…”

Mammals from the earliest Uintan (middle Eocene) Turtle Bluff Member, Bridger Formation, southwestern Wyoming, USA, Part 3: Marsupialia and a reevaluation of the Bridgerian-Uintan North American Land Mammal Age transition

“…Of the two dated samples in this study, the date of sample PCM3Aug14-04 from the tuffaceous white sandstone bed is in close agreement with the U-Pb date of the Sage Creek Mountain tuff by Tsukui (2016), and the two ages overlap within analytical error. These two U-Pb dates are also in agreement with the 40 Ar/ 39 Ar date of Smith et al (2008Smith et al ( , 2010 for the Sage Creek Mountain tuff when the astronomically calibrated age of the Fish Canyon sanidine is used, although the 40 Ar/ 39 Ar date is comparatively older. Based on the age as well as the description of the bed from which the sample was collected, it is likely that the Sage Creek Mountain tuff of Smith et al (2008Smith et al ( , 2010 and Tsukui (2016) is the same bed as the bed from which PCM3Aug14-04 was collected.…”

“…These two U-Pb dates are also in agreement with the 40 Ar/ 39 Ar date of Smith et al (2008Smith et al ( , 2010 for the Sage Creek Mountain tuff when the astronomically calibrated age of the Fish Canyon sanidine is used, although the 40 Ar/ 39 Ar date is comparatively older. Based on the age as well as the description of the bed from which the sample was collected, it is likely that the Sage Creek Mountain tuff of Smith et al (2008Smith et al ( , 2010 and Tsukui (2016) is the same bed as the bed from which PCM3Aug14-04 was collected. The best age estimate for the Ui1a fauna in the TBM is thus provided by the radioisotopic (U-Pb and 40 Ar/ 39 Ar) dates from the level of Locality SDSNH 5844 (Roll the Bones) as well as the stratigraphically lower tuffaceous white sandstone bed and the apparently laterally equivalent Sage Creek Mountain tuff.…”

“…The new radioisotopic data provide important constraints for the age of the TBM as well as its Ui1a fauna. The new U-Pb dates are generally consistent with the U-Pb and 40 Ar/ 39 Ar ages of ash beds from the Bridger Formation in Smith et al (2008Smith et al ( , 2010 and Tsukui (2016). Of the two dated samples in this study, the date of sample PCM3Aug14-04 from the tuffaceous white sandstone bed is in close agreement with the U-Pb date of the Sage Creek Mountain tuff by Tsukui (2016), and the two ages overlap within analytical error.…”

Evolution of an organic‐rich lake basin – stratigraphy, climate and tectonics: Piceance Creek basin, Eocene Green River Formation

“…The lake types discriminated by Smith et al. (2008) correlate well with isotope data (after Pitman, 1996) where the Piceance Creek basin formed as a fresh to brackish water basin at the beginning of its evolution (Stage 1), but was saline for most of the rest of the time (Stages 2 to 6).…”

Fossilisation of Fish Soft Tissue in Oxidative Microniches of Anoxic Sediments

“…This composition is indicative of a carbonate‐dominant system, consistent with the mineralogy of the Fossil Basin and broader GRF (Hellawell and Orr 2012; Smith et al. 2008; Tuttle 1991). The predominant carbonate deposition of the GRF has been attributed to high pH levels in the lake system (Grande 2013; Smith et al.…”

Mammals from the earliest Uintan (middle Eocene) Turtle Bluff Member, Bridger Formation, southwestern Wyoming, USA, Part 3: Marsupialia and a reevaluation of the Bridgerian-Uintan North American Land Mammal Age transition

“…Of the two dated samples in this study, the date of sample PCM3Aug14-04 from the tuffaceous white sandstone bed is in close agreement with the U-Pb date of the Sage Creek Mountain tuff by Tsukui (2016), and the two ages overlap within analytical error. These two U-Pb dates are also in agreement with the 40 Ar/ 39 Ar date of Smith et al (2008Smith et al ( , 2010 for the Sage Creek Mountain tuff when the astronomically calibrated age of the Fish Canyon sanidine is used, although the 40 Ar/ 39 Ar date is comparatively older. Based on the age as well as the description of the bed from which the sample was collected, it is likely that the Sage Creek Mountain tuff of Smith et al (2008Smith et al ( , 2010 and Tsukui (2016) is the same bed as the bed from which PCM3Aug14-04 was collected.…”

“…These two U-Pb dates are also in agreement with the 40 Ar/ 39 Ar date of Smith et al (2008Smith et al ( , 2010 for the Sage Creek Mountain tuff when the astronomically calibrated age of the Fish Canyon sanidine is used, although the 40 Ar/ 39 Ar date is comparatively older. Based on the age as well as the description of the bed from which the sample was collected, it is likely that the Sage Creek Mountain tuff of Smith et al (2008Smith et al ( , 2010 and Tsukui (2016) is the same bed as the bed from which PCM3Aug14-04 was collected. The best age estimate for the Ui1a fauna in the TBM is thus provided by the radioisotopic (U-Pb and 40 Ar/ 39 Ar) dates from the level of Locality SDSNH 5844 (Roll the Bones) as well as the stratigraphically lower tuffaceous white sandstone bed and the apparently laterally equivalent Sage Creek Mountain tuff.…”

“…The new radioisotopic data provide important constraints for the age of the TBM as well as its Ui1a fauna. The new U-Pb dates are generally consistent with the U-Pb and 40 Ar/ 39 Ar ages of ash beds from the Bridger Formation in Smith et al (2008Smith et al ( , 2010 and Tsukui (2016). Of the two dated samples in this study, the date of sample PCM3Aug14-04 from the tuffaceous white sandstone bed is in close agreement with the U-Pb date of the Sage Creek Mountain tuff by Tsukui (2016), and the two ages overlap within analytical error.…”

Evolution of an organic‐rich lake basin – stratigraphy, climate and tectonics: Piceance Creek basin, Eocene Green River Formation

“…The lake types discriminated by Smith et al. (2008) correlate well with isotope data (after Pitman, 1996) where the Piceance Creek basin formed as a fresh to brackish water basin at the beginning of its evolution (Stage 1), but was saline for most of the rest of the time (Stages 2 to 6).…”

Fossilisation of Fish Soft Tissue in Oxidative Microniches of Anoxic Sediments

“…This composition is indicative of a carbonate‐dominant system, consistent with the mineralogy of the Fossil Basin and broader GRF (Hellawell and Orr 2012; Smith et al. 2008; Tuttle 1991). The predominant carbonate deposition of the GRF has been attributed to high pH levels in the lake system (Grande 2013; Smith et al.…”

Mammals from the earliest Uintan (middle Eocene) Turtle Bluff Member, Bridger Formation, southwestern Wyoming, USA, Part 3: Marsupialia and a reevaluation of the Bridgerian-Uintan North American Land Mammal Age transition

“…Of the two dated samples in this study, the date of sample PCM3Aug14-04 from the tuffaceous white sandstone bed is in close agreement with the U-Pb date of the Sage Creek Mountain tuff by Tsukui (2016), and the two ages overlap within analytical error. These two U-Pb dates are also in agreement with the 40 Ar/ 39 Ar date of Smith et al (2008Smith et al ( , 2010 for the Sage Creek Mountain tuff when the astronomically calibrated age of the Fish Canyon sanidine is used, although the 40 Ar/ 39 Ar date is comparatively older. Based on the age as well as the description of the bed from which the sample was collected, it is likely that the Sage Creek Mountain tuff of Smith et al (2008Smith et al ( , 2010 and Tsukui (2016) is the same bed as the bed from which PCM3Aug14-04 was collected.…”

“…These two U-Pb dates are also in agreement with the 40 Ar/ 39 Ar date of Smith et al (2008Smith et al ( , 2010 for the Sage Creek Mountain tuff when the astronomically calibrated age of the Fish Canyon sanidine is used, although the 40 Ar/ 39 Ar date is comparatively older. Based on the age as well as the description of the bed from which the sample was collected, it is likely that the Sage Creek Mountain tuff of Smith et al (2008Smith et al ( , 2010 and Tsukui (2016) is the same bed as the bed from which PCM3Aug14-04 was collected. The best age estimate for the Ui1a fauna in the TBM is thus provided by the radioisotopic (U-Pb and 40 Ar/ 39 Ar) dates from the level of Locality SDSNH 5844 (Roll the Bones) as well as the stratigraphically lower tuffaceous white sandstone bed and the apparently laterally equivalent Sage Creek Mountain tuff.…”

“…The new radioisotopic data provide important constraints for the age of the TBM as well as its Ui1a fauna. The new U-Pb dates are generally consistent with the U-Pb and 40 Ar/ 39 Ar ages of ash beds from the Bridger Formation in Smith et al (2008Smith et al ( , 2010 and Tsukui (2016). Of the two dated samples in this study, the date of sample PCM3Aug14-04 from the tuffaceous white sandstone bed is in close agreement with the U-Pb date of the Sage Creek Mountain tuff by Tsukui (2016), and the two ages overlap within analytical error.…”

Evolution of an organic‐rich lake basin – stratigraphy, climate and tectonics: Piceance Creek basin, Eocene Green River Formation

“…The lake types discriminated by Smith et al. (2008) correlate well with isotope data (after Pitman, 1996) where the Piceance Creek basin formed as a fresh to brackish water basin at the beginning of its evolution (Stage 1), but was saline for most of the rest of the time (Stages 2 to 6).…”

Fossilisation of Fish Soft Tissue in Oxidative Microniches of Anoxic Sediments

“…This composition is indicative of a carbonate‐dominant system, consistent with the mineralogy of the Fossil Basin and broader GRF (Hellawell and Orr 2012; Smith et al. 2008; Tuttle 1991). The predominant carbonate deposition of the GRF has been attributed to high pH levels in the lake system (Grande 2013; Smith et al.…”